Can a defendant invoke the Fifth Amendment privilege against self-incrimination?

A criminal defendant is obliged to assist the authorities "[u]nless his silence is protected by the privilege against self-incrimination." Roberts v. United States, 445 U.S. 552, 558, 100 S.Ct. 1358, 1363, 63 L.Ed.2d 622 (1980). The privilege must be invoked in a timely fashion, unless the Government has substantial reason to believe that the requested disclosure is likely to be incriminating. See id. at 559, 100 S.Ct. at 1363-64. Dallas did not invoke the Fifth Amendment privilege until he raised it on appeal.